The present invention relates to a circuit arrangement for precharging an intermediate circuit capacitance of a high-voltage on-board power supply system. In particular, the present invention relates to a circuit arrangement that manages with few connections and by means of which the switching times of a high-voltage MOSFET used for charging the intermediate circuit capacitance can be reduced.
The electrification of personal individual transport is currently advancing rapidly. In order to generate the necessary power (very high currents are required at 12 V, which would require copper cables with a cross section that is not sensible in practice), a voltage level (for example 400 volts) that is increased significantly compared to 12-volt on-board power supply systems is conventionally used. The intermediate circuit capacitance transmits energy between an energy store (for example a fuel cell) and one or more electric motors, which is/are used as traction machine/machines. Traction machines are often embodied in a three-phase manner. When the high-voltage on-board power supply system is put into operation, first of all a ground-side contactor is closed, the intermediate circuit capacitance is charged to approximately 99% by means of a limited current and only subsequently is the positive contactor closed. In this way, wear and losses as well as impairments of the function of the positive contactor can be reduced or prevented.
A high-voltage MOSFET is conventionally used for precharging the intermediate circuit capacitance. In order to keep the losses and the development of heat even within the high-voltage MOSFET low, the high-voltage MOSFET has to establish the electrical connection with the lowest possible electrical resistance very quickly. Switching times of below 600 nanoseconds are desirable. The main task of the conventionally used high-voltage MOSFET is to conduct and to switch the precharging current. In order to arrive as quickly as possible at a safe state after the precharging current has been switched off, the switch-off process has to be carried out particularly quickly.
US 2015/0256014 A1 discloses a circuit arrangement for switching a precharging current for a high-voltage on-board power supply system. In a battery control device, first of all a ground contactor then an insulated-gate transistor for actuating a high-voltage MOSFET are closed in order to charge the intermediate circuit capacitance to 99%. The precharging current is limited here by means of an external precharging resistor. The positive battery contactor is then closed.